Further ring openings and ring expansions of phosphetans

Abstract

Further ring openings and ring expansions of phosphetans are described. Attempts to generate the ylide from 1,2,2,3,4,4-hexamethyl-1-phenylphosphetanium iodide led to ring opening via pentacovalent intermediates as also did the action of cyanide ion on this salt. Ring expansions of 2,2,3-trimethyl- and 2,2,3,3-tetramethyl-1-phenylphosphetan on reaction with ethyl propiolate in wet ether, on reaction with dimethyl acetylenedicarboxylate, and on hydrolysis of the iodomethylphosphetanium salts, occur with migration of the methylene and/or the isopropylidene group. 2,2,3-Trimethyl- and 2,2,3,3-tetramethyl-1-phenylphosphetan oxides are readily hydrolysed with dilute alkali with ring opening to give phosphinic acids.